1. Field of the Invention
This invention relates to improved optical or imaging systems for use in electro-optical color printers and method for using such an optical system.
2. Description Relative to Prior Art
A typical electro-optic printer comprises a printhead having a plurality of point-like electro-optic recording elements, such as light emitting diodes (LEDs) for providing a source of light and a refractive optical system for focusing or imaging the light emitted by such LEDs on a photosensitive material. In known color printers for recording on color photographic film or paper, several LEDs are used that emit light with different spectral content. The LED light is typically red, blue and green.
When a single refractive imaging system (also called a lens system) is used to focus light beams of different wavelengths, such a lens system is likely to suffer from color aberrations. Correction of color aberrations in a lens system requires additional lens elements and also often requires the use of expensive glass materials. In addition, a typical printer application requires that the lens system have a low F number to ensure sufficient light for exposure. A low F number is also difficult to achieve without having a large number of lens elements. Thus, a lens system having a low F number and, which is also color corrected, is complex, has many optical elements and is usually expensive to manufacture.
An alternative solution is to use multiple lens systems, where each lens system focuses different color beams. Not only are multiple lens systems expensive, but they also have to be aligned with respect to each other and each of them has to be aligned to the photosensitive medium.